Hallucinogenic compounds in the form of, or extracted from, plants and mushrooms have been used for centuries, mostly in religious rituals. Almost all hallucinogens contain nitrogen and are classified as alkaloids. Many hallucinogens have chemical structures similar to those of neurotransmitters (e.g., acetylcholine-, serotonin-, or catecholamine-like) and temporarily interfere with their action or bind their receptor sites, but the exact mechanisms by which these substances exert their hallucinogenic effects remain unclear. The most common types of hallucinogens are:

  • LSD (d-lysergic acid diethylamide) is one of the most potent mood-changing chemicals. It was discovered in 1938 and is manufactured from lysergic acid, which is found in ergot, a fungus that grows on rye and other grains.
  • Peyote is a small, spineless cactus in which the principal active ingredient is mescaline. This plant has been used by natives in northern Mexico and the southwestern United States as a part of their religious rites. Mescaline can also be produced through chemical synthesis.
  • Psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine) is obtained from certain types of “magic” mushrooms that are indigenous to tropical and subtropical regions of South America, Mexico, and the United States. These mushrooms typically contain less than 0.5 percent psilocybin plus trace amounts of psilocin, another hallucinogenic substance.
  • PCP (phencyclidine) was developed in the 1950s as an intravenous anesthetic, but this use has been discontinued due to serious adverse effects.

How are hallucinogens abused?

The very same characteristics that led to the incorporation of hallucinogens into ritualistic or spiritual traditions have also led to their propagation as drugs of abuse. Importantly, and unlike most other drugs, the effects of hallucinogens are highly variable and characteristically unreliable, producing different effects in different people or at different times. This is mainly due to the significant variations in amount and composition of active compounds, particularly in the hallucinogens derived from plants and mushrooms. Because of their unpredictable nature, the use of hallucinogens can be particularly dangerous.

  • LSD is sold in tablets, capsules, and, occasionally, liquid form; thus, it is usually taken orally. LSD is often added to absorbent paper, which is then divided into decorated pieces, each equivalent to one dose. The experiences, often referred to as “trips,” are long; typically, they begin to clear after about 12 hours.
  •  Peyote. The top of the peyote cactus—also referred to as the crown—consists of disc-shaped buttons that are cut from the roots and dried. These buttons are generally chewed or soaked in water to produce an intoxicating liquid. The hallucinogenic dose of mescaline is about 0.3 to 0.5 grams, and its effects last about 12 hours. Because the extract is so bitter, some prefer to prepare a tea by boiling the cacti for several hours.
  •  Psilocybin. Mushrooms containing psilocybin are available fresh or dried and are typically taken orally. The active psilocin (4-hydroxy-N,N-dimethyltryptamine) and psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine) cannot be inactivated by cooking or freezing preparations. Thus, they may also be brewed as a tea or added to other foods to mask their bitter flavor. The effects of psilocybin, which appear within 20 minutes of ingestion, last approximately 6 hours.
  • PCP is a white crystalline powder that is readily soluble in water or alcohol. It has a distinctive bitter chemical taste. PCP can be mixed easily with dyes and turns up on the illicit drug market in a variety of tablets, capsules, and colored powders. It is normally snorted, smoked, or ingested. For smoking, PCP is often applied to a leafy material such as mint, parsley, oregano, or marijuana. Depending upon how much and by what route PCP is taken, its effects can last approximately 4–6 hours.

How do hallucinogens affect the brain?

LSD, peyote, psilocybin, and PCP are drugs that cause hallucinations, which are profound distortions in a person’s perception of reality. Under the influence of hallucinogens, people see images, hear sounds, and feel sensations that seem real but do not exist. Some hallucinogens also produce rapid, intense emotional swings. LSD, peyote, and psilocybin cause their effects by initially disrupting the interaction of nerve cells and the neurotransmitter serotonin. Distributed throughout the brain and spinal cord, the serotonin system is involved in the control of behavioral, perceptual, and regulatory systems, including mood, hunger, body temperature, sexual behavior, muscle control, and sensory perception. PCP, on the other hand, acts mainly through a type of glutamate receptor in the brain, important for the perception of pain, responses to the environment, and memory. There have been no properly controlled research studies on the specific effects of these drugs on the human brain, but smaller studies and several case reports have been published documenting some of the effects associated with the use of hallucinogens:

  • LSD. Sensations and feelings change much more dramatically than the physical signs. The user may feel several different emotions at once or swing rapidly from one emotion to another. If taken in large enough doses, the drug produces delusions and visual hallucinations. The user’s sense of time and self is altered. Experiences may seem to “cross over” different senses, giving the user the feeling of hearing colors and seeing sounds. These changes can be frightening and can cause panic. Some LSD users experience severe, terrifying thoughts and feelings of despair, fear of losing control, or fear of insanity and death while using LSD. LSD users can also experience flashbacks, or recurrences of certain aspects of the drug experience. Flashbacks occur suddenly, often without warning, and may occur within a few days or more than a year after LSD use. In some individuals, the flashbacks can persist and cause significant distress or impairment in social or occupational functioning, a condition known as hallucinogen-induced persisting perceptual disorder (HPPD). Most users of LSD voluntarily decrease or stop its use over time. LSD is not considered an addictive drug since it does not produce compulsive drug-seeking behavior. However, LSD does produce tolerance, so some users who take the drug repeatedly must take progressively higher doses to achieve the state of intoxication that they had previously achieved. This is an extremely dangerous practice, given the unpredictability of the drug. In addition, cross-tolerance between LSD and other hallucinogens has been reported.

  • Peyote. The long-term residual psychological and cognitive effects of mescaline, peyote’s principal active ingredient, remain poorly understood. A recent study found no evidence of psychological or cognitive deficits among Native Americans that use peyote regularly in a religious setting. It should be mentioned, however, that these findings may not generalize to those who repeatedly abuse the drug for recreational purposes. Peyote abusers may also experience flashbacks.
  • Psilocybin. The active compounds in “magic” mushrooms have LSD-like properties and produce alterations of autonomic function, motor reflexes, behavior, and perception. The psychological consequences of psilocybin use include hallucinations, an altered perception of time, and an inability to discern fantasy from reality. Panic reactions and psychosis also may occur, particularly if a user ingests a large dose. Long-term effects such as flashbacks, risk of psychiatric illness, impaired memory, and tolerance have all been described in case reports.
  • PCP. The use of PCP as an approved anesthetic in humans was discontinued in 1965 because patients often became agitated, delusional, and irrational while recovering from its anesthetic effects. PCP is a “dissociative drug,” meaning that it distorts perceptions of sight and sound and produces feelings of detachment (dissociation) from the environment and self.
  • First introduced as a street drug in the 1960s, PCP quickly gained a reputation as a drug that could cause bad reactions and was not worth the risk. However, some abusers are attracted by feelings of strength, power, and invulnerability as well as a numbing effect on the mind that PCP can induce. Among the adverse psychological effects reported are:

    Symptoms that mimic schizophrenia, such as delusions, hallucinations, paranoia, disordered thinking, and a sensation of distance from one’s environment.

    Mood disturbances: For example, approximately 50 percent of individuals presenting for drug-induced problems in an emergency room setting and meeting criteria for PCP use in the past 48 hours reported significant elevations in anxiety symptoms.

    People who abuse PCP for long periods of time report memory loss, difficulties with speech and thinking, depression, and weight loss. These symptoms can persist up to a year after stopping PCP abuse.

    Addiction: PCP is addictive—its repeated abuse can lead to craving and compulsive PCP-seeking behavior, despite severe adverse consequences.

    What other adverse effects do hallucinogens have on the brain?

    Unpleasant adverse effects as a result of the use of hallucinogens are not uncommon—one of the reasons is that there are often a large number of psychoactive ingredients in any single source of hallucinogen.

    • LSD. The effects of LSD depend largely on the amount taken. LSD causes dilated pupils; can raise body temperature and increase heart rate and blood pressure; and can cause profuse sweating, loss of appetite, sleeplessness, dry mouth, and tremors.
    • Peyote. Its effects can be similar to LSD’s, including increased body temperature and heart rate, uncoordinated movements (ataxia), profound sweating, and flushing. The active ingredient mescaline has also been associated, in at least one report, to fetal abnormalities.
    • Psilocybin. It can produce muscle relaxation or weakness, ataxia, excessive pupil dilation, nausea, vomiting, and drowsiness. Individuals who abuse psilocybin mushrooms also risk poisoning if one of the many existing varieties of poisonous mushrooms is incorrectly identified as a psilocybin mushroom.
    • PCP. At low to moderate doses, physiological effects of PCP include a slight increase in breathing rate and a pronounced rise in blood pressure and pulse rate. Breathing becomes shallow; flushing and profuse sweating, generalized numbness of the extremities, and loss of muscular coordination may occur. At high doses, blood pressure, pulse rate, and respiration drop. This may be accompanied by nausea, vomiting, blurred vision, flicking up and down of the eyes, drooling, loss of balance, and dizziness. PCP abusers are often brought to emergency rooms because of overdose or because of the drug’s severe untoward psychological effects. While intoxicated, PCP abusers may become violent or suicidal and are therefore dangerous to themselves and others. High doses of PCP can also cause seizures, coma, and death (though death more often results from accidental injury or suicide during PCP intoxication). Because PCP can also have sedative effects, interactions with other central nervous system depressants, such as alcohol and benzodiazepines, can also lead to coma.

    Source courtesy of: The National Institute on Drug Abuse